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    <title>Document</title>
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    <script type="text/javascript">
        //1.        
                 function fn(a){
                    this.a = a
                }
                    var obj={};
                    var getNum = fn.bind(obj);
                    getNum(2);
                    console.log(obj.a);//2
        
        //2.
                 function fun(n,o) {
                    console.log(o);
                    return{
                        fun:function (m) {
                            return fun(m,n)
                        }
                    }
                }
        
                var a= fun(0);a.fun(1);a.fun(2);a.fun(3);// undefined ；  0 ； 0 ；0；
                var b= fun(0).fun(1).fun(2).fun(3);//undefined 0 1 2 
                var c= fun(0).fun(1);c.fun(2);c.fun(3);//undefined  0 1 1
        
        //3.使用递归求到20的斐波那契数列之和
                function num(n) {
                    if (n==20) {
                        return 20;
                    }
                    return n+num(n+1)
                }    
                console.log(num(0));
        
            </script>
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